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CHAPTER
4
Antisepsis, Disinfection, and
Sterilization
George Byrns
Learning Objectives
1. Define terms used in antisepsis, disinfection, and sterilization
2. Identify the major types of germicides used in health care.
3. Discuss the importance of hand hygiene and CDC’s current
recommendations
4. Identify types of sterilization methods used to reprocess
medical equipment and supplies
5. Discuss the importance of matching the germicide with its
intended use
6. Review the functions of central services, housekeeping, and
linen and laundry
In this chapter, we will describe uses and limitations of certain germicidal
chemicals and processes. A key to the prevention of healthcare-acquired infections is appropriate disinfection and sterilization of instruments and equipment (Rutala 1996). However, in order to achieve our infection prevention
objectives, there are some critical points to remember. First, there is no such
thing as a perfect germicide. In the selection of a germicide, we must frequently balance efficacy (the ability to destroy microbes) with safety of people
and products. If a germicide is capable of destroying bacteria spores, but in
the process, an expensive instrument is damaged, the approach is obviously
not acceptable. One approach to protecting heat-sensitive instruments was to
use ethylene oxide as a sterilizing agent. However due to environmental and
occupational hazards and long cycle times, some newer, low-temperature sterilization systems have been developed. Examples of these approaches include
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HAZARD RECOGNITION AND CONTROL IN INSTITUTIONAL SETTINGS
hydrogen peroxide vapor, chlorine dioxide gas, ozone gas, peracetic acid liquid,
mixed chemical/gas-plasma, and hydrogen peroxide gas-plasma (Favero and
Bond 2001). The second consideration is examining the application and intention of the germicide. It is not necessary or desirable to achieve sterility in all
instances. While surgical implants must be sterile, most environmental surfaces,
like floors, need only to be clean. Even surfaces that come in contact with mucus
membranes do not need to be sterile; they need to be free of disease-causing
microorganisms. The key is to match the desired task with the most appropriate
type of germicide. A final point is that cleaning (the removal of all foreign materials) is a critical step in either disinfection or sterilization (Rutala 1996).
CLASSIFICATION OF GERMICIDES
There are two broad classifications of germicides: antiseptics and disinfectants.
Antiseptics are used on living tissue, whereas disinfectants are used on inanimate
objects. Another distinction is that disinfectants used on medical equipment
are regulated by the Food and Drug Administration (FDA), whereas other disinfectants are considered pesticides and regulated by the Environmental
Protection Agency (EPA). Certain chemicals, such as alcohol, tincture of iodine
(a mixture of alcohol and iodine), and iodophor (a chemical solution of iodine
and a solubilizing agent), may be both antiseptics and disinfectants, depending
on the concentration. The potential confusion from overlapping jurisdictions
led the two agencies to sign a Memorandum of Understanding in which the
FDA took responsibility for regulation of liquid chemicals used for high-level
disinfection or sterilization, and the EPA took responsibility to regulate general
purpose disinfectants. The Centers for Disease Control and Prevention (CDC)
is not a regulatory body, but it does provide some guidance on the use of germicides in the prevention of nosocomial infections (CDC 2003).
Types of Disinfection
With the exception of prions (a transmissible form of an abnormal protein),
bacterial spores are most difficult to kill, and vegetative bacteria and lipid
viruses are easiest to kill. E.H. Spaulding proposed three levels of germicidal
action: high, intermediate, and low (Favero and Bond 2001). High-level disinfectants are expected to kill vegetative bacteria, Mycobacterium tuberculosis (TB),
some spores, fungi, and viruses. Intermediate-level agents kill vegetative bacteria, TB, fungi, viruses, but are not expected to kill bacterial spores. Low-level
agents kill most vegetative bacteria, fungi, and lipid viruses. They will not
destroy spores or non-lipid viruses, and they are sometimes less active against
TB or gram negative rods such as Pseudomonas sp.
Examples of Disinfectants by Germicidal Activity
High-level disinfection is the minimum level recommended by the CDC for
reprocessing semicritical instruments (CDC 2003). See the classification of
devices below.
Antisepsis, Disinfection, and Sterilization
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Some examples of high-level germicides are:
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8% formaldehyde
2% glutaraldehyde
100% ethylene oxide gas (EtO)
10–20% stabilized hydrogen peroxide
58% hydrogen peroxide plasma
0.55% ortho-phthalaldehyde (OPA)
Some examples of intermediate-level germicides are:
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70–90% alcohol
䊏 0.1–0.5% chlorine
䊏 phenolic
䊏 0.01–0.007% iodophor
An example of a low-level is quaternary ammonium compounds (quats).
Classification of Devices
Critical devices have a substantial risk of causing an infection because they are
used in procedures that enter sterile tissue or the vascular system (Favero and
Bond 2001). Some examples of critical devices are surgical implants, heart-lung
oxygenerators, needles, scalpels and other surgical instruments. Semicritical
devices do not ordinarily penetrate body tissues but may come in contact with
mucous membranes. Some examples of semicritical devices are flexible endoscopes, laryngoscopes, endotracheal tubes, other similar instruments. Noncritical devices or surfaces are expected to only touch intact skin. These devices
may be subcategorized into medical equipment surfaces with routine patient
contact and housekeeping surfaces with little to no patient contact. Some
examples of noncritical devices or surfaces are stethoscopes, tabletops, bed
railings, floors, walls, and ceilings.
Matching Devices to Processes
All evidence suggests that the most important issue in destroying potentially
pathogenic microorganisms in instruments such as endoscopes is cleanliness
and not the level of germicidal activity (Favero and Bond 2001). Thorough
decontamination and cleaning must precede either sterilization or disinfection for any process to be considered reliable. The reason that cleaning is most
important is that residual biofilm or other organic matter can shield microbes
from the germicide. Also, the mechanical action of cleaning can remove a
large number of microbial contaminants.
Critical Items. These devices present a high risk of infection; usually, steam
sterilization is the most efficacious means of reprocessing critical instruments.
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HAZARD RECOGNITION AND CONTROL IN INSTITUTIONAL SETTINGS
While steam is the cheapest and most effective means of achieving sterility,
certain heat-labile equipment must be reprocessed using other means. The
minimum level of treatment for heat-labile critical instruments is high-level
disinfection, and preferably sterilization (Favero and Bond 2001). Chemical
germicides that are sporicidal take much longer time to achieve sterility than
steam sterilizers, in some cases, as long as 24 hours.
Semicritical Instruments. For heat-stable semicritical instruments, steam
sterilization may be the most cost-effective means of reprocessing (Favero and
Bond 2001). On the other hand, heat-labile semicritical instruments typically
do not enter sterile tissue, so sterility is not required. If the instrument can not
withstand long contact with a chemical germicide, high-level disinfection is
sufficient. It should be noted that the primary difference between sterilization
and high-level disinfection when using chemical germicides is the amount of
contact time.
Noncritical Items. Since noncritical items offer little risk of infection, the
main issue is cleanliness and not disinfection. Medical equipment surfaces may
frequently become contaminated during patient procedures, so it is prudent to
use low- to intermediate-level germicide on these surfaces. Housekeeping surfaces would not be expected to play a role in nosocomial infections. Some
authorities suggest that to be on the safe side, even housekeeping surfaces
should be disinfected (Rutala and Weber 2001b). This issue is controversial,
and others believe that detergents or low-level disinfectants are appropriate
(Favero and Bond 2001). The major exception is laboratory culture or blood
spills. These require special precautions. The following steps are recommended to handle these types of spills:
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Don a pair of disposable gloves
Remove excess fluids using absorbent materials such as paper towels
Dispose of the absorbent materials in a red bag
Use any germicide labeled as a “hospital disinfectant” to clean the area
Characteristics of a Good Germicide
As previously stated, there is no such thing as the perfect germicide. When
selecting a germicide, consider the following issues:
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Biocidal properties: Will the germicide kill those organisms of concern?
䊏 Applicable to intended use: Will the germicide be efficacious without
harming people or the objects being disinfected?
䊏 Contact time: How long does it take for the germicide to do the
intended job?
䊏 Employee acceptance: Will the employees find the germicide easy and safe
to use, and are there any unpleasant odors or staining problems
associated with its use?